Unattended repeater system



Oct. 29, 1935i, E A. um i 2,018,859

i UNATTENDED REPEATER SYSTEM Filed June 9, 1954 2 lSheets-Shes?, l

LE X- S-ziyzjw Sezcz'zn 2 Sgaitnlfm 3 Scn Y CTL I w a -1212iL 3l @l L Y HZaJm, w m'. v W

lll-v n "lll-In- X Ime 7 zine 2 n zi 3 zine Y Sectdan, Sectrlon Sectllon y'gctzlmrr, @mi :1 Lit wl; j 'W .Elarm/ w v Illl l f, Il Elim l v l l f @L h l INVENTOR BY ATTORNEY F. A. LEIBE UNATTENDED REPEATER SYSTEM Filed June 9, 1954 2 Sheets- Sheet 2 @MMN y, Zz'e BY 1 ATTORNEY Patented Oct. 29, 1935 UNITED STATES UNATTENDED REPEATER SYSTEM Frank Augustus Leibe, Quakertown, Pa., assignor to American Telephone and Telegraph Company, a corporation of New York Application June 9, 1934, Serial No. 729,921

10 Claims.

This invention relates to transmission systems and more particularly to systems involving unattended repeater stations.

In the development of new types of transmis- 5 sion systems, particularly those employing wide ranges of frequencies, it is desirable to employ repeaters spaced at more frequent intervals. Because of the large number of repeaters involved, it is desirable that some of the repeaters be left l unattended especially as repeaters have been developed which are sumciently reliable in performance to be left unattended in suitable housings for considerable periods of time.

Regardless of the degree of reliability which is 15 attained in the development of such unattended repeaters, however, the possibility of an occasional failure can never be entirely ruled out. Where more than one unattended repeater is employed between adjacent attended stations,

20 it is desirable, in the event of failure of one of the unattended repeaters, to have available some means whereby the attendant at an attended repeater station may readily determine which unattended repeater is inoperative. It is one of Zl the purposes of the present invention to provide facilities whereby this information may be obtained at attended repeater points.

The indication at the attended repeater poin may be based upon the ability of the unattended 30 repeater to amplify (a) the voice, television, or other signals transmitted; or (b) the indication may be based upon the ability of the amplifier to transmit a pilot frequency or frequencies.

In a system having so few communication 35 channels superimposed on it that the signals passing through the unattended repeater will be intermittent in character, it would be preferable to base the indication upon a pilot frequency or frequencies which are continuously trans- 40 mitted.

Various types of signaling systems for indicating failure of a repeater and for determining the location of the repeater which has failed, may be provided. For example, the system may be 45 arranged to transmit continuously through the unattended repeaters an alternating current which may be either the normal signaling currents passing over the system or a special pilot frequency. Each unattended repeater may be 50 so related to a direct current path common to all of the unattended repeaters of the group, that upon failure of the repeater to operate, a change will be produced in the condition of the direct current path thereby producing a signal at an 5 attended repeater station, The fillldant upon observing the signal may then test over the direct current path to determine the point at which the change in condition has occurred, as, for example, by making resistance measurements.

The invention may also be embodied in an ar- 5l rangement in which, when the repeater fails, the location of the repeater may be indicated at an attended station directly, without the necessity of any. testing operation. For example, instead of using a direct current path a plurality of pilot frequencies, one corresponding to each unattended repeater, may be transmitted over the circuit from the attended station through the Various unattended stations. Each unattended station is arranged to exercise control over the l5 pilot frequency assigned to that particular station, and upon the failure of a particular unattended repeater that repeater will be identified by the fact that the pilot frequency corresponding thereto produces no indication at the indicating point.

Also, the invention may. be embodied in an arrangement in which, instead of transmitting separate pilot frequencies or other signaling currents for testing purposes over each one-way transmission circuit of a two-Way system, as is contemplated in the arrangements above described, a combined indicating arrangement for both directions may be used. For example, failure of the unattended repeater for either direction at a given repeater station may be caused to produce at an attended repeateran indication of the station at which the failure hastaken place. An additional signal individual to each directional pathv and common to all of the un- 35 attended repeaters in tandem in that path, may be used to indicate failure of any repeater in the path'. By means of the two indications the individual repeater which has failed may be ascer-tained. 40

Only arrangements corresponding to the third type of system above mentioned, are disclosed herein. Systems of the first type are disclosed and claimed in the joint application of E. I. Green and F. A. Leibe, Serial No. 729,922 filed June 9, 1934. Systems of the second type above described, are disclosed and claimed in a joint application of E. I. Green and F. A. Leibe, Serial No. '729,923 led June 9,- 1934.

The invention will now be more fully understood from the following detailed description thereof when read in connection with the accompanying drawings in which Figures 1, 2 and 3 illustrate three embodiments of a system for indicating the location of an unattended repeater 55 that has failed in a two-way system employing a combined indicating arrangement for both directions of transmission.

Referring to Fig. l, LE designates a portion of the transmission circuit transmitting from transmission passes through the repeater EAX the rectifier ERX recties a portion of the received transmission and thereby energizes a relay. The

received currents to be rectified may be either i normal signaling currents or, as previously stated, Where the number of channels normally transmitted is too small to assure that some signal will be transmitted at all times, a pilot frequency may be transmitted over the line LE to hold up the relay. If the repeater EAX or any portion of the transmission circuit ahead of said repeater should fail, there will be no current in the output of the rectifier ERX and the relay will be released-to actuate the alarm signal ESX. At station Y a similar rectifier ERy is associated through a transformer with the output of an attended repeater EAy and controls through its relay an alarm signal ESy. The operation of the alarm ESy will indicate failure of the repeater EAX, or failure inthe circuit ahead of the repeater EAy. At stations I, 2 and 3 unattended repeaters EUi, EUz and EUa are inserted inthe line LE.

The line LW is provided with transmission equipment similar to that described in connection with the line LE, including anattended repeater WAY, an associated rectifier WRX, and an alarm WSy at'station Y. It also includes an attended repeater WAX an associated rectier WRX and an alarm WSX at stationrX. The actuation of the alarm WSy at station Y indicates failure at station Y or some point to the east thereof, and failure of operati-on of the alarm WSX at station X indicates failure at station X or some point to the east thereof. Intermediate repeaters WUi, WUz and WUs areconnected with the line LW at the points, I, 2 and 3, respectively.

In order to indicate failure of an unattended station and to enable `the attendant at the attended stationto locate theV position of the repeater which has failed, provision is made for applying certain testing frequencies to the system so that these frequenciesl will be transmitted over certain sections of the lines LE and LW in tandem.V For this purpose generators-XGi, XG2 and XG-i generating frequencies f1, f2 and fa, are connected to the line LE at station X on the out-v put side of the repeater EAX. The corresponding receiving equipment is bridged across the line LW at the point b of station X. This receiving equipment comprises three filters F individually selective of frequencies f1, f2 and fa and three corresponding rectifiers R which rectify the selected frequencies and cause the operation of direct current indicators in the output circuits of the rectiers. i

At station I a cross-connection is established between the output circuit of repeater EUi in y line LE to the input circuit of the repeater W01 inline LW through a filter F1 which is selective of the frequency f1. At station 2 a similar crossconnection extends from the output of repeater EU2 to the input of repeater WUs through filter F2 selective of frequency f2. So also, at station 3, a cross-connection extends from the output of the unattended repeater EUa to the input of the unattended repeater WUs through a filter Fa selective of the frequency fa. The filters included in these cross-connections should be made very sharply selective (as, for example, by using one or more crystal elements) in order to avoid introducing crosstalk between the oppositely directed transmissions. The loss in each filter for the passed frequency should be made substantially equal to the lossof one line section between the repeaters, as otherwise the frequency passed 'through the filter would arrive at the input of the repeater on the return side of the circuit `without any loss in amplitude and might overload the repeater. By making the loss4 of the filter about equal to that of one line section the passed frequency transmitted from the path in one direction, across to the return path in the other direction, will arrive at the latter with about the same amplitude it would have, had it been transmitted over a line section to a succeeding repeater.

With the arrangement above described, the frequency f1 will pass from station X, over the first line section of line LE, through the repeater EU1, across the cross-connection including the filter F1, back through the repeater WUi, over the line section of line LW to the station X, and thence into its proper signal indicating circuit through the filter F which is selective 'of frequency fi. Similarly, the frequency f2 is transmittedfrom the point w at station X, through the repeaters EU1 and EUz, thence across the cross-connection including filter F2 and back through repeaters WU2 and W'Ui to the point b at station X. So also, the frequency fa is transmitted fromV the point a, through repeaters EUi, EU2 and EUa, thence across the cross-connection through filter F3 and back through repeaters WUs, WUz and WU1, to point b.

It will now be evident that the failure of different repeaters will be indicatedvas set forth in the following chart.

It will be noted that the indication given in the foregoing chart only tells the attendant at station X the unattended repeater station at which a repeater has failed. For example, if the repeater EUX should 'fail frequencies f2 and f3 would not be received, but the attendant would not know whether it was the repeater EUn or WUz which had failed as the failure of either of these repeaters would result in] blocking frequencies f2 and f3. However, the attendant by lascertaining that the alarm ESy at station Y had indicated that the trouble'was on the line LE, would know that it was the repeater EUn which had failed. In practice, however, it may prove desirable, when a repeater fails on the line transmitting in one direction, to replace not only that repeater but the repeater at the same station on the line transmitting in the opposite di- Vattended repeater stations.

recticn, in which case the indication givenl in,

of the line section immediately preceding it. Itv

would be possible to distinguish between these two types of failures by a D. C. test made in thev manner ordinarily Vemployed forA telephone` cables.

The arrangement of Fig. l involves a` scheme in which three frequencies serve for indications in both directions of transmission for three un- Fig. 2 illustrates an arrangement similar to that of Fig. 1,. except that only two frequencies are employed instead of three. The arrangement of the repeaters in Fig. 2 is identical with that of Fig. 1, and so also, the rectiiers and alarm arrangements associated with the outputs of the four attended repeaters at stations X and Y are identical with those shown in Fig. 1. The application of the testing frequency is, however, somewhat different. A generator XG1 generating a frequency f1 is connected to the line LE at the point a at station X, and a bridge is connected at the point c of the line LE at station Y, said bridge including parallel filters F selective of frequencies f1 and f2, respectively, said filters being connected to corresponding rectiflers R having direct current indicators in their output circuits. Similarly, a generator YG'2 generating a frequency f2 is connected at d to the line LW at station Y,

Y while a bridge circuit is connected at point b to the line LW at station X. Said bridge circuit includes parallel filters F selective of frequencies f1 and f2, and associated rectiers and indicators identical with those at station Y.

The cross-connections between the two sides of the circuit in Fig. 2 are also somewhat different from those of Fig. 1. For example, a cross-connection including a iilter F1 selective of frequency f1 is bridged from the output side of repeater EU1 at station i to the input side of repeater WU1 at station I. Another cross-connection is'bridged from the' output side of repeater WUa at station 3 to the input side of repeater EUa at station 3, this cross-connection` including a filter F3 selective of frequency f2. No cross-connection is established at repeater station 2.

'Ihe frequency f1 is transmitted from point a over the first line section of line LE and through the repeater EU1 at the output of which it divides, part flowing over the remainder of the line including the repeaters EUz and EU, into the filter F at station Y selective of the frequency f1. Part of the energy of frequency f1 on the output side of repeater EU1 flows thro-ugh the filter F1, through the westbound repeater VifUl, and over the line section of LW to point b where it enters the bridge and passes through the filter F selective of the frequency f1 at station X. Similarly, the frequencf,7 f2 is transmitted from the point d in the line LW at station Y, over one section of the line and through the repeater WUs Where the energy is divided, part of it passing on over the line LW through the repeaters WUz and WU1, to the point b where it enters the bridge connection and passes through the filter F selective of the frequency f2. The other part of the energy of frequency f2 on the output side of the repeater WUs passes through the filter F3 in the cross-connection to the input side of the repeater EUS, through said repeater and over a line section of line LE to the point c where it enters the bridge connection and passes through the filter F selective of frequency f2 at station Y.

Inspection of this arrangement will show that the indications provided are as follows:

Thus a knowledge of the frequencies received at the two ends of the circuit in Fig. 3 permits an exact determination of the location of failure as between. all six of the unattended repeaters involved. It has a slight disadvantage, however, that the attendant at one of the attended stations X or Y, mus-t ascertain from the attendant at the other of said stations what frequencies are being received there before having the necessary information to identify the location of the failure.

In the arrangements which have been described in Figs. 1 and 2, the testing frequencies have been passed through or around the unattended repeaters without being used to produce new frequencies or combinations of frequencies at such points.

Fig. 3 shows an arrangement in which the test frequencies are modulated at certain of the unattended repeater points in. order to secure new frequencies or combinations. This affords an advantageous method of obtaining indications where the number of unattended repeaters ina section is large, and where it is desired to limit the number of test frequencies employed. Thus, for example, in Fig. 3 there is illustrated an arrangement in which two. different frequencies f1 and f2 serve to furnish indications for a total of six unattended repeater stations involving a total of' twelve repeaters. This result is obtained by a method similar to. .that of Fig. l, except that combinations of frequencies f1 and f2. (fiel-f2, 2f1+f2, etc.) are derived at certain vof the unattended repeaters.

In Fig. 3 frequencies f1 and f2 are applied tothe line LE at the point a at station X. At the point b` of line LW at station X a bridge circuit is connected in which six parallel filters F, one corresponding to each unattended repeater point, are arranged. These filters are selective of frequencies f1, f2, fri-f2. fi-fa 2J1-l-f'2 and 21H-f2. A cross-connection is provided at un" attended repeater station i between the output of repeater EU1 and the input of repeater WUr, said cross-connection including the filter F1, selective of frequency f1. A simiiar cross-connection is made at unattended repeater station through the lter F2 selective of frequency f2. At unattended repeater station 3 a cross-connection extends from the output of repeater EUS to the input of repeater WU3. This cross-connection includes a filter F3 which selects both frequencies f1 and f2. On the output side of the filter is a modulator M3 which modulates the two frequencies f1 and f2. On the output side Yof the modulator is another filter Fa which selects from the various components in the output of the modulator M3, the particular frequency fri-'fz which passes back to the point b through the repeaters WUs, WUz and WU1. At the unattended repeater station 4 is a cross-connection similar to that shown at station 3, except that in this case the filter F21 is selective of the modulation component fi-fz which is transmitted back over line LW through repeaters WU4 to WU1, inclusive. At unattended repeater station 5 is a cross-connection similar to that at station 3, except that the filter F5 selects the modulation component 2f1-l-2 which passes back to the point b through the repeaters WU5 to WU1, inclusive. At station 6 is still another cross-connection similar to that of station 3, except that the filter F's selects the modulation component 2f1f2 which is transmitted back over the line LW through all siX unattended repeaters.

Inspection of the arrangement of Fig. 3 will show that the indications provided are as follows:

Frequencies received at b Inoperative EUs or WUs EUg 0r WU: EUi or WU1 lthe attendant at station Y whether the line indicators show that the fault is on line LE or on line LW.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different .from those illustrated, without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1. In a signaling system, a pair of transmission lines transmitting in opposite directions between attended stations, a plurality of unattended repeater stations between said attended stations and each having repeaters in each of said transmission lines, means to apply a plurality of test frequencies to said transmission lines, cross-connections between said transmission lines so associated with said lines as to form different paths over portions of said lines for said test frequencies, said cross-connections being so located with respect to said unattended repeater stations and the repeaters thereat that different frequency paths will be disabled upon the failure of repeaters at different unattended repeater stations, and indicating means associated with the ends of said test frequency paths to indicate the failureof particular paths, whereby the combination of paths which are indicated as not having failed will serve to identify the unattended repeater station at which a repeater has failed.

2. In a signaling system, a pair of transmission lines transmitting in opposite directions between attended stations, a plurality of unattended repeater stations between said attended stations and each having repeaters in each of said transmission lines, means to apply a plurality of test frequencies to said transmission lines, cross-connections between said transmission lines so associatedwith saidlines as to form different paths over portions of said lines for said test frequencies, said cross-connections being so located with respect to said unattended repeater stations and the repeaters thereat that different frequency paths will be disabled upon the failure of re- 5 peaters at different unattended repeater stations, indicating means associated with the ends of said test frequency paths to indicate the failure of particular paths, whereby the combination of paths which are indicated as not having failed will serve 10 to identify the unattended repeater station at which a repeater has failed, and means associated with said transmission lines at attended stations to indicate that a failure has occurred ahead of an attended station. 15

3. In a signaling system, a pair of transmission lines transmitting in opposite directions between attended stations, a plurality of unattended repeater stations between said attended stations and each having repeaters in each of said transmission 20 lines, means to apply a plurality of test frequencies to said transmission lines, cross-connections between said transmission line at each unattended repeater station, each cross-connection being selective of a different frequency so as to form dif- 25 ferent paths over portions of said lines for test frequencies, said cross-connections being so located with respect to said unattended repeater stations and the repeaters thereat that failure of a repeater at a particular unattended repeater 30 station results in disabling the path of a test frequency characteristic of that station, and indicating means associated with the ends of said test frequency paths to indicate the failure of particular paths, whereby-the combination of paths 35 which are indicated as not having failed will serve to identify the unattended repeater station at which a repeater has failed.

4. In a signaling system, a pair of transmission lines transmitting in opposite directions between 4,0 attended stations, a plurality of unattended repeater stations between said attended stations and each having repeaters in each of said transmission lines, means to apply a plurality of test frequencies to said transmission lines, cross-connections a between said transmission lines at each unattended repeater station, each cross-connection being selective of a different frequency so as to form different paths over portions of said lines for test frequencies, said cross-connections being so lo- 5a cated with respect to said unattended repeater stations and the repeaters thereat that failure of a repeater at a particular unattended repeater station results in disabling the path of a test frequency characteristic of that station, indicating means 5| associated with the ends of said test frequency paths to indicate the failure of particular paths, whereby the combination of paths which are indicated as not having failed will serve to identify the unattended repeater station at which a re- 30 peater has failed, and means associated with said transmission lines at attended stations to indicate that a failure has occurred ahead of an attended station.

5. In a signaling system, a pair of transmission lines transmitting in opposite'directions between attended stations, a plurality of unattended repeater stations between said attended stations and each having repeaters in each of said trans- 70 mission lines, means to apply to one of said transmission lines at one attended station a plurality of test frequencies equal in number to said unattended repeater stations, there being one frequency characteristic of each unattended repeater station, indicating means associated with the other of said transmission lines rat said attended station, said indicating `means being selectively indicative of the failure of the frequency characteristic of any unattended repeater station, and cross-connections between said transmission lines at each unattended repeater station, each cross-connection being selective of a different frequency so as to form different paths over portions of said lines for said test frequencies, whereby the combination of frequencies indicated as not having failed will serve to identify an unattended repeater station at which a repeater has failed.

6. In a signaling system, a pair of transmission lines transmitting in opposite directions between attended stations, a plurality of unattended repeater stations between said attended stations and each having repeaters in each of said transmission lines, means to apply to one of said transmission lines at one attended station a plurality of test frequencies equal in number to said unattended repeater stations, there being one frequency characteristic of each unattended repeater station, indicating means associated with the other of said transmission lines at said attended station, said indicating means being selectively indicative of the failure of the frequency characteristic of any unattended repeater station, cross-connections between said transmission lines at each unattended repeater station, each cross-connection being selective of a different frequency so as to form different paths over portions of said lines for said test frequencies, whereby the combination of frequencies indicated as not having failed will serve to identify an unattended repeater station at which a repeater has failed, and means associated with said transmission lines at attended stations to indicate that a failure has occurred ahead of an attended station.

7. In a signaling system, a pair of transmission lines transmitting in opposite directions between attended stations, a plurality of unattended repeater stations between said attended stations and each having repeaters in each of said transmission lines, means to apply to one of said transmission lines at one attended station a plurality of test frequencies less in number than the number of unattended repeater stations, crossconnections between said transmission lines at each unattended repeater station, certain of said cross-connections being selective of said test frequencies and other of said cross-connections having means to produce and being selective of other frequencies derived from said test frequencies so that there will exist different paths over said lines for different frequencies characteristic of each unattended repeater station, and indicating means associated with the other of said transmission lines at said attended station, said indicating means being selectively indicative of the failure of the frequency characteristic of any unattended repeater station, whereby the combination of frequencies indicated as not having failed will serve to identify an unattended repeater station at which a repeater has failed.

8. In a signaling system, a pair of transmission lines transmitting in opposite directions between attended stations, a plurality of unattended repeater stations between said attended stations and each having repeaters in each of said transmission lines, means to apply to one of said transmission lines at one attended station a plurality of test frequencies less in number than the number of `unattended .repeater stations, cross-connections between said transmission lines at each unattended repeater station, certain of said cross-connections being selective ofsaid test frequencies and other of said cross-connections having means to ,produce and being selective of other frequencies derived from said test frequencies so that there will exist different paths over said lines for different frequencies characteristic of each unattended repeater station, indicating means associated with the other of said transmission lines at said attended station, said indicating means being selectively indicative of the failure of the frequency characteristic of any unattended repeater station, whereby the combination of frequencies indicated as not having failed will serve to identify an unattended repeater station at which a repeater has failed, and means associated with said transmission lines at attended stations to indicate that a failure has occurred ahead of an attended station.

9. In a signaling system, a pair of transmission lines transmitting in opposite directions between attended stations, a plurality of unattended repeater stations between said attended stations and each having repeaters in each of said transmissionlines, means to apply to one of said transmission lines at one attended station a test frequency, a cross-connection between said transmission lines at an unattended repeater station, said cross-connection being selective of said test frequency so as to provide a return path for said test frequency back to said attended station over the other transmission line as well as a path to the second attended station over said first trans- 'mission line, means to apply to said second transmission line at said second attended station a attended stations as not having failed will serve to 50 identify an unattended repeater which has failed.

l0. In a signaling system, a pair of transmission lines transmitting in opposite directions between attended stations, a plurality of unattended repeater stations between said attended stations and each having repeaters in each of said transmission lines, means to apply to one of said transmission lines at one attended station a test frequency, a cross-connection between said transmission lines at an unattended repeater station, said cross=connection being selective of said test frequency so as to provide a return path for said test frequency back to said attended station over the other transmission lineas well as a path to the second attended station over saidflrst transmission line, means to apply to said second transmission line at said second attended station a second test frequency, a cross-connection between with each of said lines at each of said attended stations to selectively indicate the reception of either or both of said test frequencies, whereby the combination o-f frequencies indicated at the two attended stations as not having failed will serve to identify an unattended repeater which has failed; and means associated with said transmission lines at attended stations to indicate that a failure has occurred ahead of an attended station.

FRANK A. LEIBE. 

